Analysis of the promoter of an abscisic acid responsive late embryogenesis abundant gene of Arabidopsis thaliana

Late embryogenesis abundant (lea) proteins are a diverse group of proteins present in many mono- and dicotyledonous plants. The genes encoding lea proteins are expressed in the embryo during the late stages of seed development. However, expression can also be induced in immature seeds and vegetative tissues by abscisic acid (ABA). Lea genes thus provide a model with which to study tissue-specific, developmental and hormonal regulation of expression. We used the beta-glucuronidase (iudA) reporter gene (gus) to identify functional domains in the promoter of a lea gene of Arabidopsis thaliana (AtEm1). We found that a promoter fragment extending from -182 bp to +72 bp is sufficient to direct gus expression to embryos and pollen of transgenic tobacco. Gus expression in embryos and pollen was developmentally regulated, being expressed during the late stages of seed and anther development. Comparison of different deletion constructs showed that in both tissues promoter sequences between -1443 bp and -430 bp had no effect on the level of gus expression, whilst the region between -430 bp and -182 bp is necessary for full level expression. The response to ABA was studied in seedlings of transgenic tobacco transformed with a gus gene fusion construct containing -1443 bp to +72 bp of promoter. Treatment with 50 mu M ABA resulted in a 3-4-fold increase in GUS activity, indicating that ABA induction of AtEm1 acts at least in part at the level of transcription. Conserved regulatory elements were identified in the promoter of AtEm1 by sequence analysis. The possible role of these elements, and the significance of the observed gus expression in pollen are discussed.